Reptilia, Biology tutorial

Features of Class Reptilia (Lizards, crocodiles, snakes, tortoises, turtles)

Reptiles are characterized by the features:

  • Dry skin with keratinised epidermal horny scales
  • Bony endoskeleton
  • Two pairs of pentadactyl (five digits) limbs with true claws (if limbs are there)
  • No external ear
  • Fertilization is internal and fertilised eggs laid (oviparous) on land or eggs retained internally until hatching (ovoviviparous)
  • Amniotic egg with leathery shell (see Figure 2.10)
  • Cold blooded (poikilothermic/exothermic)
  • Gut and the ducts of the urinary and reproductive system open into a posterior chamber called the cloaca.

There are approx 6,550 living species of reptiles worldwide; they live in the wide range of habitats, comprising grasslands, forests, mountains, deserts, swamps and oceans. Name reptile is usually applied to any of the group of ectothermic (cold-blooded that is need outside source of heat to create adequate body heat) vertebrates in Class Reptilia. Reptiles contain dry and not moist skin. They are covered in scales or the shell. If they contain legs, they have true claws on their toes. Reptiles can be far from water sources as their skin preserves water better than that of amphibians. Reptiles lay amniotic eggs which have leathery shell which prevents rapid water loss.

Class Reptilia is made up of four orders that is Order Crocodilia (crocodiles and alligators), Order Testudinata (turtles), Order Squamata (lizards and snakes) and Order Rhynchocephalia (Tuataras).

Features of Order Crocodilia (Crocodiles and alligators)

  • Contain a long snout
  • Four well-developed limbs
  • The muscular tail utilized to propel them through water
  • Lay eggs in large mounded nests or in cavities dug in soil
  • Carnivorous on fish, reptiles, amphibians, mammals and birds.

Crocodile contains very long, narrow, V-shaped snout, while alligator's snout is wider and U-shaped. A crocodile's upper and lower jaws are almost the same width, so teeth are exposed all along jaw line in the interlocking pattern, such that even when mouth is bottom teeth are visible. Alligator's teeth do not show when its mouth is closed.

Features of Order Testudinata (Turtles and tortoises)

  • Shell or carapace formed from the fusion of vertebrae and ribs with dermal bones
  • No teeth but contain sharp-edged beak, known as a tomium utilized as cutting edges to bite off chunks of food
  • Oviparous and fertilization internal and accomplished by the penis that is outgrowth of cloacal wall. Eggs are buried in thenest and left to incubate and hatch.
  • No temporal opening in skull behind eye, condition called as anapsis. This caharcteristics is unique among living reptiles.

Shell of turtle/tortoise comprises of two fundamental parts, top shell that is referred to as carapace, and the bottom shell which is called as a plastron. Ribs and vertebrae of turtle/tortoise, with exception of neck and tail, are fused to make carapace. Latin word-root test is for shell, and order name "Testudines" is Latin for turtle. Tortoises are considered as turtles which live in land and have un-webbed feet unlike water turtle which survive most of the lives in water and have webbed feet. The two are thus differentiated by their habitat that is land turtle or water turtle.

Features of Order Squamata (Lizards and snakes)

They have transverse vent or cloacal opening, skull is more moveable (or kinetic) than other reptile orders, paired copulatory organs known as hemipenes, body covered in scales, occasionally shed their skin (the process called as ecdysis/moulting), carnivorous or omnivorous, diversity of habitats (aquatic, terrestrial, or arboreal).

The Order Squamata (meaning scaled reptiles) is the largest order of reptiles with more than 6,000 living species. It is most varied of reptile orders, comprising 96% of reptile species. They are signified by Lacertilia (lizards) and Serpentes (snakes). Members of this enormous order are found worldwide. Several squamates have loss or reduction of limbs and skill to lose tail (caudal autotomy). Snakes contain the elongate body (some lizard species are limbless and contain long slender bodies). On the other hand, lizards (Lacertilia) are characterized by 4 limbs (few lizards species which lack limbs), visible ear openings, and movable eyelids.

Monitor lizards are large reptiles (few are small as 20 cm long). They contain long neck, strong tails and claws, and well developed limbs. The majority species are terrestrial but few aquatic species are also known. They are generally carnivorous though some eat fruit. Monitor lizards are oviparous, laying 7-37 eggs that are buried in soil or protect in hollow tree stump.

Features of Order Rhynchocephalia (Tuatara)

  • third primitive, light-sensitive eye above brain
  • dwell in burrows and are nocturnal, hunting at night only outside their burrow entrance
  • They feed on lizards, worms, millipedes and small seabirds.

Tuatara signifies spiny back. Tuataras are reptiles but they are different from lizards, snakes, and crocodiles. They are lonely, nocturnal hunters of insects and small vertebrates. Tuataras develop to 60 centimeters (24 inches) in length. They may dwell more than 50 years; their eggs should incubate for 15 months before hatching-longer than for any other reptile. Scaly loose skin which may be soft to touch.

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